Assistance and advice for a MVHR project outside UK

[carphatian]

Hello all!

 

First I would like to thank all of you for the amazing content that you put together on this forum. I was reading a lot of threads during the last two weeks and I learned a lot about the MVHR. I am not yet an expert so for this reason I would like to ask your advice for designing an MVHR system.

 

We are traveling a lot for work and last year we got an assignment in Vienna, Austria. Since we are planning to stay for at least 10 years in here, we decided to buy a property and to renovate it.

 

It is a 110 m2 house built in 1965 with solid 40 cm brick walls, renovated in 2018 with 20 cm graphite EPS insulation (facade),  triple glazed windows, ceiling and screed also insulated . We did not run a blow test on it but it looks like it is pretty tight built (I am sure not perfect....). The previous owner told us that the insulation is very effective but the downside of it is that the house is not "breathing" like before. We had a ventilation system in our property in UK and I really want to install one in this house since we have two kids and I think the indoor air quality is super important.

 

We contacted a local company to do the project and they quoted us 12000 EUR using a Zehnder q350 system and Heatpex Aria piping. However after we have started they got back to us and they wanted to increase the project cost with almost 9000 EUR at which point I said no and decided to try to complete the project by myself. I am confident in doing all the installation by myself and I already made the holes in the concrete ceiling plate and installed the vents, each of them having two ports for 90mm pipes.

 

I attached a plan of the house with the installed air vents locations (this was provided by the original vendor) and the proposed piping connections. I did the calculations for the air flow requirements best of my knowledge and using the info from this forum but I still have some questions, as expected.... In Austria I do not need to go through an approval process from the construction authorities so I am pure and simple looking to design a good system that will fit the purpose. I am sure that you will have good feedback on this based on your experience.

 

I would like to get your advice on the following:

 

1. Based on my calculations the intake flow is approx 76 m3/h and the exhaust is approx 113 m3/h. For the system to be balanced these values should be the same so obviously I will need either to increase the flow of the air coming in or reduce the exhaust. My question is in which location should I do this.

 

2. The kitchen and living room are actually a shared space. There are two intake and two exhaust vents on each side of the shared space. Should the flow for these vents be the same so the air flow is balanced for this location?

 

3. In general I am planning to run one 90mm pipe to each of the air vent. Based on my calculation for the velocity and distance I should be OK with this. The distribution boxes for this systems have eight connecting ports (so 8 for intake and 8 for exhaust) so theoretically I could double the pipes for 3 intake and 3 exhaust vents. I was thinking to do this for at least the bathroom exhaust and Bedroom 2 which are 3m long. It will be great if you could tell me if this is enough.

 

4. The original vendor planned an exhaust on the hallway (not a humid space) which might provide a good air movement from the bedrooms. In my opinion this is logical for me but I would love to hear your opinions. The vent is already installed so the worst I could to is to change it to an intake but the distance between this vent and the exhaust in the WC might create a local air motion only.

 

5. The kitchen already has a hood vent installed above the stove with exhaust outside the building. I would like to keep it if possible and start it on during heavy cooking only. I know this will create an imbalance between the intake and exhaust but I was wondering if this might be OK for short periods of time only. Otherwise I will have to remove the hood cover the exhaust hole in the wall and install a re-circulation/filtration hood.

 

I apologize for all the questions and I hope I can contribute a bit to the knowledge collection in here.

 

Thank you!

 

 

Ventilation Plan.pdf MVHR calculation.xlsx

[JohnMo]

You want 40 in a double and 20 in a single bedroom.

 

 

Dump the hall extract, not needed, unless you need to balance the numbers. Use Passivhaus numbers.

 

Kitchen extract put both ducts to a single extract point - no value having two, keep 9. Lounge area the same one terminal, keep 4.

 

Normal flow area, multiply 2.5, multiply 0.3. so normal flow about 83m³/h, boost multiply by 1.2.

[carphatian]

Thank you John.

 

Advice well received about dumping the three terminals (kitchen, living room and hallway).

 

I am still a bit confused about the calculation. Based on the entire space volume I will need approx 84 m3/h flow. This is more or less what I used for each room in my Excel to calculate for the fresh air intake 0.3 ACH per room in column M. I calculated 0.3 l/s /m2 but it is close.

 

Using the passive house guidelines for a 4 person household I will need 120 m3/h fresh air but calculating on volume only 84 m3/h which is a big difference. Now taking the bedrooms, based on their size it is tough to consider them single or double. But let's say the two bedrooms of approx 15m2 in which there will be double beds I can consider "double" and the small 12 m2 "single". Based on this guidelines I will need 100 m3/h just for the bedrooms, which will leave 20m3/h (out of the 120 m3/h) left for the living room. For example one of the big bedrooms has a volume of 38 m3 so calculating 0.3 ACH, I will need a flow of 11.4 m3/h. Even if I consider it a single bedroom based on the guidelines I will need 20 m3/h which will bring the ACH to approx 0.5.

 

For the three spaces requiring extract (kitchen, bathroom and WC) I will need 92 m3/h extract rate. If I consider all the three bedrooms as single I will then need 60m3/h fresh air and to balance the numbers I will then setup the fresh air in the living room to 32 m3/h? This without taking in consideration the 120m3/h fresh air requirement...

 

Since the kitchen and the living room share the same space, should the kitchen extract (46m3/h) match the intake for the living room or it will be OK to live it at 32 m3/h?

 

I really have the feeling that I am overthinking some of these aspects. But I am a bit perfectionist and I am sailing on uncharted waters for me here...

 

Thank you again for your patience!

 

 

 

[JohnMo]

Simple way to think about and you have given the answer - use the most demanding airflow. So if 4P is greater than 0.3ACH, you use the 4P

 

Double single rooms - how many people will sleep in the room - nothing to do with area. Small bedroom with bunk beds is a double room, no matter how big or small. Treat guest rooms as a single or split the difference.